The invention relates to a drive-slip control device for motor vehicles in which, when a driven vehicle wheel spins, this wheel is braked and when both driven wheels spin, engine power is also reduced. Spinning of the drive wheels is recognized by means of rotational-speed sensors and an electronic system and, when a spin signal is present on account of a differential-speed threshold value between driven and non-driven vehicle axle being exceeded, the power of the engine is reduced in a controlled manner by the electronic system during the duration of the spin signal by means of a final control element. When the spin signal ceases, the power of the engine is increased again in a controlled manner to a target value predetermined by the driver by means of the accelerator.
A drive-slip control device of this general nature can be found (German OffenLegungsschrift 3,544,294)the object of which is generally to prevent uncontrolled spinning of the drive wheels when a vehicle is being started on a smooth base.
The spinning of the wheels is sensed by wheel rotational-speed sensors and is evaluated in the electronic system. If only one wheel spins, the associated wheel brake is actuated (differential brake) via a brake control valve. A drive moment is thereby transmitted via the wheel differential to the other non-slipping wheel.
If both drive wheels spin, however, the power of the driving engine is reduced in a controlled manner. To this end, the throttle linkage is operated to reduce the value set by the driver.
The engine control by the drive-slip control device thus normally comes into effect when there is a certain differential speed between the driven and non-driven vehicle axles. If the speed again drops below this speed differential threshold, the engine over-ride control is switched off and the power of the engine is again increased in a controlled manner to the value predetermined by the driver via the accelerator pedal.
During gear-shift operations in particular, when the engine control by the drive-slip control device works before gear disengagement, it is found that after the reengagement and acceleration, the known engine control function of the drive-slip control device is not always able to absorb the excess power occurring. Correspondingly, high slip amplitudes can occur and thus lead to instability of the vehicle. This applies equally when power is reduced by easing back on the accelerator and when the throttle is again opened immediately afterwards and without a gear-shift operation. This corresponds, to a shock reaction or a speed adaption.
The object of the invention is to design a drive-slip control device of the above general nature in such a way that the travelling stability of the vehicle is also ensured during gear shift operations as mentioned above.
This object is achieved when the predetermined driver accelerator target value falls back during an engine control operation of the drive-slip control device to or below the instantaneous control target value reached at an instant during the control operation because of a gear shift. This instantaneous control target value reached at that instant is recorded and is used for the final controlling control element. The instantaneous control target value also corresponds to the instantaneous accelerator target value at that instant. The recorded instantaneous control target value is stored for a predetermined time. After the power falls back during reacceleration after the gear shift, the control operation to increase power (by the presetting of a new accelerator target value) follows the accelerator target value only when the stored instantaneous control target value is reached after a predetermined time period, whereas it follows the engine-control target value trend when the stored instantaneous control target value is reached within the predetermined time period.
The invention here starts from the consideration that the transmittable power, e.g. before and after a gearshift operation is about the same, when the condition of the roadway remains stable, so that the value for maximum power after a gear-shift operation should be that value which was present before the gear-shift operation after an engine control operation of the drive-slip control device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.